The present invention relates to a transmitter and method for transmitting coded signals over a channel which may have changing characteristics over time and, more particularly, to a transmitter, transmission system and method wherein characteristics of the channel are substantially continually detected, a code technique is selected based on the characteristics and the signals arc coded in the selected code technique.
In a current communications system, information is processed and converted to electrical signals on an originating end of the system (such as a transmitter). The electrical signals are then transmitted over a communications channel to a receiving end of the system (such as a receiver). The receiver then processes the electrical signals and converts the signals back into the information. Numerous factors influence the speed, efficiency and reliability of the communication process. One significant factor is whether the communication channel is changing over time. The characteristics of the channel are especially prone to be changing if the transmitter, receiver or both are moving.
In an effort to reduce errors caused by changes in the characteristics of the channel, the electrical signals are often coded with special error detection and correction information. One example of a well known error detection technique is the use of cyclical redundancy checking (CRC) code. Two examples of well known error correction (often called forward error correction, or FEC) techniques are convolutional coding and repetition coding. A number of other coding techniques are also known in the art. For ease of description and clarity, the present invention will be described using only the CRC coding and the FEC coding techniques. Those skilled in the art will readily understand, however, that any of the known coding techniques may be advantageously employed in the present invention.
The performance level of each of the coding techniques is dependent upon the characteristics of the channel. In other words, some coding techniques perform better on a noisy channel while other techniques perform better on a quiet channel. Unfortunately, as noted above, the characteristics of a channel may be changing over time, especially with respect to mobile communications and the like. Prior transmitters are designed to implement a single predetermined coding technique during a transmission of information. These prior transmitters are therefore unable to accommodate these changing channel characteristics and, therefore, may experience less than optimal, or desired, performance.
Accordingly, there is a need in the art for a transmitter, method and transmission system for transmitting information which detects characteristics of a channel, selects a proper coding technique based on the detected channel characteristics, codes the information using the selected coding technique and transmits the coded information.